Degradation of an azo dye by sodium hypochlorite in aqueous surfactant solutions

The degradation behaviour of sodium 1-(2-methylphenylazo)-2-hydroxy-3,6-naphthalenedisulphonate (o-TR) by sodium hypochlorite solution in the presence of three kinds of surfactants, viz. dodecytrimethylammonium bromide (DTAB), sodium dodecylsulphate (SDS), and sodium 2-(dodecylmethylamino)-ethane-1-sulphonate (SDAS) was investigated by means of visible absorption spectrum measurements. The degradation rate of o-TR was markedly dependent on the head groups of the surfactants. DTAB containing a quaternary ammonium head group significantly enhanced the degradation rate. SDS containing a sulphate head group enhanced the rate below the critical micelle concentration (CMC), whereas if did not change above CMC. SDAS containing a tertiary amino and suphonate group immediately degraded the dye existing outside of the micelle formed by SDAS, while the dye solubilized into the micelle remained without degradation. (C) 1998 Elsevier Science Ltd.